One reason why supernatural ghost films are so terrifying is simple: ghosts may actually exist. Ghosts pop up everywhere in popular culture, but the ideology behind them has its roots deep in history. The belief in life beyond death and hauntings started in ancient Mesopotamia and Egypt, then grew over time, as did ghost traditions and superstitions around the world. It's difficult to ignore the numerous accounts of ghost and poltergeist sightings, so readers beware: some of these tales may seem a bit too realistic for comfort.